1. Field of the Invention
This invention relates to an armature used in a small-sized motor, and more particularly to improvements in the technique of fusing treatment of a riser and a coil in order to electrically connect a coil to a commutator segment.
2. Related Art Statement
As a commutator provided with a countermeasure for gasohol, there is one in which a protective member made of a silver-nickel alloy is clad on a surface of a copper base of the segment, at least at portion which contacts brushes (refer to Japanese Utility Model Application Laid-Open Nos. 60-135053 and 62-132670, for example).
Now, if silver is used in the protective member, then the cost is increased, so that, as described in Japanese Patent Application Laid-Open No. 58-207840, there is proposed a carbon commutator wherein a copper segment is solidly secured to a boss portion formed integrally with synthetic resin and carbon plated by copper is soldered onto the segment.
With the above-described commutator, in applying the fusing treatment, in which a coil of an armature core is guided around a riser formed integrally with the copper segment, such a practice is commonly used that the riser is made to be a main electrode portion and the carbon jointed to the segment is made to be an auxiliary electrode portion, electric current is supplied therethrough to peel off an insulating film of the coil and to weld the coil to the riser (Refer to the hypothetical lines in FIG. 2).
However, in the fusing treatment in the above-described carbon commutator, a solder layer for bonding the carbon to the copper segment is included in the current passage route, whereby, when the time of applying current is lengthened, there is a possibility that the solder layer is melted so that the carbon comes off the copper segment.